1. Field of the Invention
This invention relates to a marine plant field survey method for surveying marine plant fields, particularly tropical and subtropical sea grass beds, for acquiring information useful for preserving the ecosystems of such fields, including information regarding marine plant distribution in the field, the degree of macrophyte coverage, and species of macrophytes at marine plant fields, and to a survey system utilizing the survey method.
2. Description of the Prior Art
Marine plant fields having large macrophyte communities play an important role as places where a great variety of fishes and shellfishes spawn and grow as well as sites that operate as water purifiers. In particular, subtropical and tropical sea grass beds are indispensable for ensuring the survival of sea turtles, dugongs and other large endangered animals.
In the conventional method of observing marine plants and degree of coverage by marine plants and other macrophytes at coastal marine plant fields, the area of the marine plant field is first estimated from photographs taken from above the sea surface (aerial photographs). Skilled divers with expert knowledge in the field then set meter-square quadrats at prescribed locations on the seabed. An underwater camera is used to photograph the quadrats from above and, in addition, the macrophytes in the quadrats are visually examined, photographed at close range, and collected as specimens for determining their species. The collected information is used to determine the species of macrophytes and their degree of coverage at the prescribed locations.
At tropical and subtropical marine plant fields, however, data reflecting the actual situation cannot be obtained by such underwater observation only at selected spots because various kinds of macrophytes differing in size and form live in such fields. At subtropical marine plant fields, moreover, some species live at a depth of more than 10 m from the sea surface, so that estimates of the habitat area based on aerial photographs include a large margin of error.
On the other hand, using divers to collect data is difficult because the divers must be highly skilled and possess expert knowledge in the field. Such people are hard to find and train. In addition, the length of time that a diver can continue to work underwater, though depending on the underwater environment and safety concerns, is severely limited, making the work highly inefficient. Another problem is that divers who differ in skill and knowledge must work individually. The objectivity of the gathered data is low in proportion. Still another is that positional information is hard to obtain with regard to the quadrats that the divers install at specific locations on the seabed.
An object of the present invention is to provide a survey method and a survey system for implementing the survey method that enable information, including positional information, to be accurately acquired directly over a wide area regarding marine plant distribution and degree of coverage and species of macrophytes at marine plant fields, while minimizing exposure of survey personnel to dangers.
Another object of the invention is to provide a marine plant field survey method and survey system that do not require a skilled diver with expert knowledge, are much safer than methods and systems requiring underwater work, and can be operated efficiently with no particular limitation on work period.
The present invention achieves these objects by providing a marine plant field survey method comprising a step of using a submarine mobile video system capable of taking images underwater to measure degree of macrophyte coverage in a marine plant field by taking wide-field images of macrophytes from above and a step of using the submarine mobile video system to discriminate species of macrophytes by taking images of macrophytes from a direction other than from above.
The invention further provides a survey system for surveying a marine plant field comprising a camera for taking wide-angle images of macrophytes from above and a camera for taking images of macrophytes from a direction other than from above.
The survey system can comprise a stationary image-taking system for taking wide-angle images of macrophytes from above and a movable image-taking system for taking images of macrophytes from a direction other than from above.
The survey system can further include a video monitor and the submarine mobile video system be linked with the monitor to enable image taking simultaneously with acquisition of information regarding the submarine mobile video system operating state and seabed state and discrimination of macrophyte coverage degree and species.
The survey system can further include three or more acoustic transponders installed on the seabed and a transceiver mounted on the submarine mobile video system and the submarine mobile video system be adapted to determine position by measuring the distance between the transceiver and each of the acoustic transponders.
The survey system can be configured so that an operator on board ship can follow the progress of the submarine mobile video system and conditions at the seabed on a monitor displaying the images taken by the camera that images macrophytes at a wide angle (around 90xc2x0) from above and the camera that images macrophytes from a direction other than from above and, based thereon, can operate a remote controller for imaging macrophytes and record the image data using an onboard video recorder.
The survey system therefore eliminates the need for skilled divers with expert knowledge, makes the survey work much safer than when conducted by divers working underwater, is under little limitation regarding length of work period, and enables survey work to be carried out with good efficiency.
Since the invention enables a survey to be conducted based on actually photographed images, the survey can be carried out with high objectivity and recorded data can be readily reexamined.
The survey system can be configured to incorporate a submarine mobile video pointing system for monitoring the location of the submarine mobile video system as it takes images, thereby enabling accurate analysis of marine plant distribution.
The above and other objects and features of the invention will become apparent from the following description made with reference to the drawings.